Question: The arithmetic sequence $(a_i)$ is defined by the formula: $a_1 = -1$ $a_i = a_{i-1} - 2$ What is $a_{2}$, the second term in the sequence?
Explanation: From the given formula, we can see that the first term of the sequence is $-1$ and the common difference is $-2$ The second term is simply the first term plus the common difference. Therefore, the second term is equal to $a_2 = a_1 - 2 = -1 - 2 = -3$.